This invention relates to multilayer ceramic capacitors, and more particularly to chip capacitors adapted to be connected directly to circuit boards.
Current electronic devices, including hybrid circuits on printed circuit boards, are making progressively increasing use of chip capacitors because of their compactness and inherent reliability.
In accordance with a conventional means for employing such capacitors, the same are provided with two or more termination portions at their edges and are mounted directly to a substrate of alumina or epoxy-filled fiberglass carrying conductive lands on the surface thereof. Solder or conductive epoxy connections are effected between the capacitors and the lands, the terminations being in direct contact with the lands. The solder or epoxy provides both electrical and mechanical connections of the article to the substrate.
Due to the differential coefficients of expansion of the various connected materials and due further to the relative fragility of the capacitors, particularly at the interface between the termination and the capacitor electrodes, a relatively high incidence of capacitor failure has been experienced despite the inherent reliability of the capacitor device.
In some applications, present methods of construction demand an attachment method that is prone to shorting, and attachment can cause one conductive epoxy joint to break due to the difference in thermal coefficient of expansion between alumina and barium titanate. This is a critical technical problem in manufacturing.
In addition, many hybrids utilize a large number of capacitors and much substrate area is lost. It would be desirable to make more efficient use of the substrate area.